Sequential Directed Ortho Metalation-Boronic Acid Cross-Coupling Reactions. A General Regiospecific Route to Oxygenated Dibenzopyran-6-ones Related to Ellagic Acid

Article abstract of DOI:10.1021/jo00012a004

A general regiospecific synthesis of dibenzopyran-6-one derivatives 1a,c and 8a-i related to ellagic acid is described (Scheme I, Table I).The sequence involves directed ortho metalation-boronation of benzamides 4 to give the arylboronic acids 5, which, upon palladium-catalyzed cross-coupling with alkoxybromobenzenes 6 leads to the biphenylamides 7.BBr3 demethylation followed by acid-catalyzed cyclization affords pyranone 8.In this manner, the naturally occurring dibenzopyranones 1a, autumnariol (1c), and the heterocyclic analogue 13 (Scheme III) were efficiently prepared.